It has been known that acrylic block copolymers each having a structure in which a methacrylic ester polymer block is bonded to each end of an acrylic ester polymer block have excellent flexibility, transparency, and weatherability and are useful in various fields. Acrylic block copolymers are molded into, for example, sheet-like articles used for films and sheets in the field of optics and for outdoor building materials. However, acrylic block copolymers do not have sufficient mechanical properties alone compared with styrene block copolymers. This limits fields of utilization thereof.
For example, polymer compositions each containing an acrylic block copolymer and an acrylic resin mainly composed of a methacrylic ester unit are reported (see PTLs 1 and 2). These polymer compositions have excellent mechanical properties compared with acrylic block copolymers alone. However, in the case where a sheet-like molded article is produced by extrusion, the tackiness of the resulting sheet-like molded article causes poor moldability, i.e., excessively strong adhesion to a chill roll, thereby reducing productivity. Alternatively, a higher viscosity of the composition causes fine grain-like irregularities on a surface of the sheet-like molded article produced by extrusion. The resulting sheet-like molded article is not satisfactory and has a room for improvement.
Furthermore, in order to improve the impact resistance of an acrylic resin mainly containing a methacrylic ester unit, resin compositions in which acrylic block copolymers are mixed with acrylic resins are reported (see PTLs 3 and 4). However, specific resin compositions disclosed in these literatures have poor flexibility. For thin walled molded articles, such as a sheet-like molded article, the application of stress is likely to cause cracking to lead to fracture. This limits fields of utilization thereof.
PTLs 5 and 6 each disclose a laminate film for another material, the laminate film being characterized by weatherability, flexibility, transparency, and so forth and serving as a sheet-like molded article composed of a composition mainly containing an acrylic block copolymer. However, these literatures do not specifically describe a method for improving various physical properties by the addition of an acrylic resin.
PTL 7 discloses a covering sheet composed of a composition containing an acrylic block copolymer and an acrylic resin. PTL 8 discloses an optical member composed of a composition containing an acrylic block copolymer. However, in the case where an acrylic block copolymer alone or a composition containing one type of acrylic block copolymer and an acrylic resin is molded by extrusion into a sheet-like molded article, fine streak-like irregularities are formed on a surface of the sheet-like molded article. So, the resulting sheet-like molded article is not satisfactory and has a room for improvement.